Cold rolled steel sheet having stabilized thin oxide film and having excellent resistance against corrosion particularly initial rust formation as well as against corrosion after lacquering

ABSTRACT

A COLD ROLLED STEEL SHEET CONTAINING AS A BASIC COMPONENTS C$0.12%, MN 0.10-1.00%, SI$0.15%, CU 0.010.20%, SB 0.01-0.20% AND CONTAINING IN CASE OF NECESSITY A SMALL AMOUNT OF ZR, MO, AND NI, WHICH STEEL SHEET HAS EXCELLENT RESISTANCE AGAINST CORROSION, PARTICULARLY INITIAL RUST FORMATION AS WELL AS CORROSION AFTER LACQUERING AND PROVIDES HIGH CORRORSION RESISTANT MATERIAL SUITABLE FOR CANS WHEN THE RATIO OF S TO P IS MORE THAN 1.

1972 TOSHIRO NISHIHARA E'I'AL 3,704,181

COLD ROLLED STEEL SHEET HAVLNCI STABILIZED THIN OXIDE FILM AND HAVING EXCELLENT RESISTANCE AGAINST CORROSION PARTICULARLY INITIAL RUST FORMATION AS WELL AS AGAINST CORROSION AFTER LACQUERING Filed May 19, 1970 3 Sheets-Sheet 1 FIG.]

Immersion Potential Curve 1' I Q 01)- g 0.1 v -0.2 -o: E -01. -o.5

Immersion Time(hr) Relation between Rust Percentage and Time for Autoreduction of Oxide Film Time for Autoreduction (min) I N VEN TOR.

Tosa IRo msmmn h memo HsFn smsyosm nnEw NOV. 28, 1972 TQSHIRO N|5H|HARA EI'AL 3,704,181

COLD ROLLED sTEEL SHEET HAVLNG STABILIZED THIN OXIDE FILM AND HAVING EXCELLENT RESISTANCE AGAINST coRRosIoN PARTICULARLY INITIAL RUST FORMATION As WELL As AGAINST CORROSION AFTER LACQUERING FIG.3

Relation between Sb.BiContent and Time for Autoreduction 0.12-0.15'/.c 7 u A o.12-o.is'/.cu

Filed May 19, 1970 3 Sheets-Sheet 2 Time for Autoreduction (hr) --(Sb] content (wt'l.) (Bi) content (wt'l.)

FIG.4

Relation between CuContent and Time for Autoreduction ().05 0.10 0.15 0.20 0.25 (Cu) content (wt'h) I NVEN'T 0R. Tosmko msm new It lbEJl'RO nsnuo smeayosm nnemn )ngmtm OYHGI Nov. 28, 1972 Filed May 19, 1970 Time for Autoreduction(hr) Time for Autoreduction (hr) TOSHIRO NISHIHARA EI'AL COLD ROLLED STEEL SHEET HAVING STABILIZED THIN OXIDE FILM AND HAVING EXCELLENT RESISTANCE AGAINST CORROSION PARTICULARLY INITIAL RUST FORMATION AS WELL AS AGAINST CORROSION AFTER LACQUERING FIG.5

3 Sheets-Sheet 3 Relation between C.Mn.Si Content and Time for Autoreduction --*'-[C] content (wtlo) *(Mh) content(wt'l-) -(Si) content(wt'/-) F-IG.6

Relation between Zr.Ni, MoContent and Time for Autoreduction [Zr] content (wt'l.)

8 fi kfit 8- g ggzggm l L L Steel (Mo) content(wt/.)

INVENTOR.

Tosamo Nmulmkn tflb jfllo Rsnuo United States Patent O 3,704,181 COLD ROLLED STEEL SHEET HAVING STABI- LIZED THIN OXIDE FILM AND HAVING EX- CELLENT RESISTANCE AGAINST CORROSION PARTICULARLY INITIAL RUST FORMATION AS WELL AS AGAINST CORROSION AFTER LACQUERING Toshiro Nishihara, Hidejiro Asano, Shigeyoshi Maeda, and Yashichi Oyagi, Kitakyushu, Japan, assignors to Nippon Steel Corporation, Tokyo, Japan Filed May 19, 1970, Ser. No. 38,827 Claims priority, application Japan, May 28, 1969, 44/ 41,464; Jan. 23, 1970, 45/ 5,717 Int. Cl. C22c 39/54 US. Cl. 148-315 3 Claims ABSTRACT OF THE DISCLOSURE A cold rolled steel sheet containing as a basic components C50.12%, Mn 0.10-1.00%, Si50.l5%, Cu 0.01- 0.20%, Sb 0.01-0.20% and containing in case of necessity a small amount of Zr, Mo, and Ni, which steel sheet has excellent resistance against corrosion, particularly initial rust formation as well as corrosion after lacquering and provides high corrosion resistant material suitable for cans when the ratio of S to P is more than 1.

BACKGROUND OF THE INVENTION The present invention relates to a cold rolled steel sheet having excellent resistance against corrosion, particularly against initial rust formation as well as against corrosion after lacquering.

The initial rust used herein means any rust formation of iron hydroxide (which transforms thereafter) observable by naked eye or a microscope, which takes place after the formation of a thin oxide film less than 100 A. on the fresh surface of iron and low alloy steels exposed to the atmospheric air.

Normally, when a steel sheet is, after rolling, subjected to mechanical workings such as drawing, expanding, cutting and grinding, a completely fresh metal surface appears, which is exposed to the atmospheric air. This exposed fresh surface is covered almost instantaneously by a thin oxide film (consisting essentially of 'y-Fe O less than 100 A. in the air.

This oxide film is not visible by the present measuring technics, and the fresh metal surface still retains completely metallic luster to the naked eye.

However, when the surface is exposed for a long period thereafter, rust formation takes place all over the whole surface in a short time in case of an ordinary low-alloy steel.

This rust formation first takes place at defects of the oxide film as mentioned above, and at its initial stage an iron oxide of high hydration is formed which progressively transforms into a higher oxide as the time passes. The formation of iron oxide is called as the initial rust formation and is visible by naked eyes or a microscope, which iron oxide extinguishes the metallic lustre as it progressively increases.

When an ordinary low-alloy steel is used after metal plating or organic coating, for example, as can production material, the steel material is usually blanked (or stamped) or cut into required shapes. The fresh surface exposed during the workings, for example, cross sections made by the cutting operation, has a very poor resistance against rust formation and in a short time the rust formation takes place which causes various difliculties in practical applications.

In order to overcome these dilficulties, it may be considered to apply an effective organic rust preventive coating to the surface, but this is not a satisfactory rust preventive method for protecting destructed portions of the coating caused during transportations after can production or during canning process. Therefore, importance of the resistance of the steel sheet by itself against the initial rust formation as a basic improvement is increasingly recognized.

The above fact is an important fact not only in the steel sheet for can production, but also in many applications in which thin gage steel sheets such as ones for automobile and electric appliances are used, particularly in applications in which commercial value of products is severely damaged.

The present inventors conducted various extensive researches and studies for developing steel sheet having excellent resistance against the initial rust formation, and have found that the nature and condition of the very thin oxide film less than A. formed on the exposed fresh surfaces of iron and low alloy steels plays an important role in prevening the initial rust formation. Namely, when a steel sheet is left in the air, an amount of moisture corresponding to the humidity in the atmospheric air Will deposit on the surface of the steel sheet, and in case of a defective oxide film a heavy rust formation is caused, while in case of a complete oxide film no rust formation is caused and the deposited moisture will wholly evaporate, causing no damage on the surface of the steel sheet.

Generally speaking, when a low-alloy steel is left in the atmosphere, the surface is more or less susceptible to red rust formation in a long run.

In the past, various methods were considered and proposed to preventing corrosion of steel by improving the steel itself, and may be classified into the following two groups. Namely, as seen in stainless steel, for example, one group of methods is to convert the steel itself into a noble metal by alloying it with corrosion resistant metals. In this case the metallic lustre is retained, but production cost is very high and thus the product is limitedly used only in special applications. The other group of methods is to prevent further progress of rust formation by the formation of dense oxide layer in a visible rust layer formed on the steel surface as seen in a series of lowalloy steels commonly called as atmosphere corrosion resistant steels. In this case the surface appearance is not regarded as important.

The cold rolled steel sheet having an excellent resistance to the initial rust formation aimed to by the present inventors has naturally different required properties from those required to stainless steels and atmosphere corrosion resistant steels.

Ordinary cold rolled steel sheets are usually subjected to a phosphate treatment and other substrate treatment for lacquering and then to lacquer coating before they are used in various applications such as automobile sheets and electrical appliances. However, for the substrate treatment for lacquering, very severe surface conditions must be met, and corrosion resistance after the lacquering is regarded as an important factor.

For improving the corrosion resistance after lacquering, all of the conventional arts are to improve the substrate treatment for enhancing properties of the substrate, and no try has been made to improve the corrosion resistance of the steel itself for enhancing the properties of lacquer coated steel sheet.

SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide a cold rolled steel sheet in which the thin oxide film formed on its surface can be rendered to be very dense and stabilized.

Another object of the present invention is to provide a cold rolled steel sheet having also good corrosion resistance after lacquering, in which a dense and stabilized thin oxide film is formable on fresh surfaces of the steel.

Still other object of the present invention is to provide a cold rolled thin gauge steel sheet suitable for cans, particularly cans for carbonated beverages, in which a dense and stabilized thin oxide film is formable on fresh serfaces of the steel.

Other objects of the present invention will be understood frm the following descriptions and the attached drawings.

One of the main features of the present invention is that 0.010.20% by weight of copper and 0.0l-0.20% by weight of antimony are added to a steel containing C 0.12%, Mn 0.11.00%, Si 50.15% with the balance being essentially iron. Without departure from the scope of the present invention at least one selected the group consisting of zirconium, molybdenum and nickel may be further added in an amount between 0.010.30%.

Another feature of the present invention is that the sulphur content is limited to -0.0150.10% and the ratio of sulphur content to phosphorus content is limited to more than 1 (S/P 1) in case of a steel sheet suitable for can production. The whole or part of the antimony content may be replaced with bismuth. In this case 0.01- 0.20% of bismuth in single or 0.01-0.20% of antimony plus bismuth may be contained.

The present steel sheets can be produced through smelting in an ordinary steel making furnace such as a convertor and ordinary hot and cold rolling and annealing. As for the annealing, a box annealing is desirable.

The steel sheet having excellent resistance against the initial rust formation according to the present invention 4 FIG. 6 is a graph showing the relation between the contents of zirconium, nickel and molybdenum in the steel sheet and the time for autoreduction of oxide films.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As mentioned before, the present inventors have found that the oxide film formed naturally on the fresh exposed surface of iron or low alloy steels plays an important role for preventing the initial rust formation, and the present inventors have made extensive studies on effects of steel compositions on the characteristics of the oxide film.

The natural oxide film formed on the fresh exposed surface in the atmosphere grows to a thickness of about 20-40 A. at most, and clarification of the structure and nature of the oxide film is not easy. However, the present inventors have succeeded in clarifying the co-relation between the oxide film and the resistance against the initial rust formation using electron diffraction technics and electro-chemical measuring technics.

Regarding an ordinary rust formation in which the rust is formed by the progress of atmospheric corrosion, it is an established theory accepted by experts that the rust formation is due to corrosion reactions in neutral solution. Based on this, the present inventors have investigated the characteristics of the oxide film using neutral solutions (sodium borate-chloric acid buffer solution of pH 7.65).

FIG. 1 shows the change by time in the natural electrode potential which appears when various steel sheets shown in Table I having natural oxide films formed in the atmosphere are immersed in the above neutral solutions.

TABLE I [Chemical compositions of specimens by weight percent] C Mn P S Base steel sheets 0. 25-0. 53 0. 006-0. 043 0. 006-0. 043 1. Sb contained. 0.25-0.53 0006-0043 0. 006-0. 043 0.05% Sb 2. Bi contained- 0. 25-0. 53 0. 006-0. 043 0. 000-0. 043 0.05% B1 3. Cu contained 0. 25-0. 53 0. 006-0. 043 0. 006-0. 043 0.10% Cu 4. Mos contained 0. 25-0. 53 0. 006-0. 043 0. 006-0. 043 0.05% Mo 6. Base steel sheet 0. 01 0. 25-0. 53 0. 006-0. 043 0. 006-0. 04 6. Sb and Mo contained.. 0. 01 0. 25-0. 53 0. 006-0. 043 0 006-0. 043 0.1% Sb+0.05% Mo 7. Bi and C11 contained" 0. 01 0. 25-0. 53 0. 006-0043 0 006-0. 043 0.1% Bi+0.l3% Cu 8. Sb and Cu contained 0. 01 0. 25-0. 53 0. 006-0. 043 0. 006-0. 043 0.1% sb+0.14% Cu is useful as steel sheets for can production, automobile steel sheet, and steel sheets for electric appliances. When an ordinary low alloy steel is used in the above applications, the steel sheet is usually applied with metal coatings such as Sn, Cr, Zn and Al or subjected to a phosphate treatment or a chromic acid treatment (in some case an organic coating is further applied).

The present inventive steel sheet may be treated similarly, but the advantage'of the present inventive steel sheet is that it is not susceptible to rust formation for a considerable period without any treatment, thus facilitating its transportion from steel makers to consumers and its storage.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing changes in immersion potentials of steel sheets of various compositions.

FIG. 2 is a graph showing the relation between the rust percentage and the time for autoreduction of oxide films.

FIG. 3 is a graph showing the relation between the contents of antimony and bismuth in the steel sheet and the time for autoreduction of oxide films.

FIG. 4 is a graph showing the relation between the copper content in the steel sheet and the time for autoreduction of oxide films.

FIG. 5 is a graph showing the relation between the contents of carbon, manganese and silicon in the steel sheet and the time for autoreduction of oxide films,

The general tendency is that a relatively noble potential of 0.2 v.-0.3 v. (U.S.S.C.E.) is observed at the initial stage of immersion and thereafter the potential lowers gradually and shows a sudden lowing after the lapse of certain period to about -0.7 v. which is near to the potential of a naked steel surface, where it again becomes constant. The initial high potential apparently corresponds to a potential observable under a condition in which an oxide film is present on the steel sheet surface, and the sudden lowering after the lapse of a certain period corresponds to the destruction (autoreduction di'ssolution) of the oxide film on the steel sheet surface. It is concluded from the above the oxide film is of more stable and less defect structure when the period for which the noble potential of about -0.3 v. is retained (the autoreduction time) is longer, and thus the resistance against the initial rust formation can be remarkably enhanced.

In FIG. 2 are shown the relation between the relation the autoreduction time and the initial rust formation percentage observable by naked eyes. It is clear from FIG. 2 that the longer the autoreduction time is (the more stable the oxide film is), the lower the initial rust formation percentage is, thus proving the above conclusion. In FIG. 2, for the rusting test, the test specimens were stacked in a humidity cabinet which was controlled at 40 C., relative humidity.

Next, the present inventors have further investigated the mechanism of prevention of the initial rust formation by the steel compositions, and have found that the alloying elements set forth in Table I in single or in combination remarkably stabilize the non-visible oxide film (mainly of 'yFe O as observed by the electron difiraction technics) formed on the steel surface.

Of the above basic composition, antimony (bismuth also similar effect) is found to have the highest effect of enhancing the resistance against the initial rust formation, and steels containing these alloying elements show more noble initial immersion potentials and longer time of oxide film destruction as compared with the steel (5 in Table I) containing none of these elements. From this it is clear that the addition of antimony reduces the defects of oxide film and increases remarkably resistance against the reduction dissolution of the film. (1 and 6 in FIG. 1). These tendencies are recognized also in the addition of bismuth (2 and 7 in FIG. 1).

The reason for limiting the contents of antimony and bismuth to a range of 0.010.20% is as seen in FIG. 3 that any substantial effect is not obtained with a content less than 0.01%, and the good effect of antimony and/or bismuth addition will saturate and the qualities of the steel sheet will be deteriorated with a content more than 0.20%. From the points of addition effects and economy, the preferrable range of antimony and/or bismuth contents is ODS-0.10%.

Copper content is an important factor in the present inventive steel sheet. Copper is an unavoidable element introduced in the steel during ordinary pig iron producing and steel making processes, and even by selective use of high-quality iron ore and advanced technics of converter steel making and so on, copper comes unavoidably into steel in a very small amount. As shown in FIG. 4, the present inventors have found that copper shows favourable effects only when it is used in combination with antimony and copper in single does not show any substantial effect. The effective range of copper content is 0.01-0.20% and the most desirable range is 0.08-0.18%. Beyond the above eifeotive range, intermetallic compounds or a phase of copper precipitate, thus causing undesirable elfects.

As a result of our basic experiments for clarifying the mechanism of resistance against the initial rust formation due to the steel compositions, it has been concluded that the effects of antimony and copper are based on the following mechanism.

During the natural formation of iron oxide film, the antimony in solid solution in the steel is also oxidized, and a part of it comes into the oxide film and contributes to constitute the film in the form of Sb but not in the form of Sb However, it is not known whether the antimony gets into the lattice of iron oxide by replacement with Fe ion or is localized as a simple oxide of Sb O in particular portions of the iron oxide, for example in the defect portions of the oxide film.

Sb ion has an oxidizing action and inhibits the reduction dissolution of the film. Namely, destruction (in a neutral solution and corresponds to atmospheric corrosion) of the film is generally takes the following autoreduction reaction:

Anodic reaction:

FeZFe H-Ze Cathodic reaction:

Fe O +3H O+2e22Fe ++6OH But under the presence of Si) ion the reaction is:

Sb ++2Fe Sb to Fe thus oxidizing Fe to Fe.

Namely in the reduction of the film which is a cathodic reaction (the reaction of Fe Fe takes place is the lattices of iron oxide and then Fe reacts with H O to produce iron hydroxide and destroys the film), even when Fe is formed in the lattice, Sb present near it oxidizes instantly it into Fe thus converting the oxide into its original state.

On the other hand, in the dissolution of iron which is an anodic reaction, Fe O is formed by the oxidizing action of Sb and fills up the defect portions of the film.

Copper which exhibits remarkable effect, particularly when added under the presence of antimony, is present in the steel in the state of solid solution, but is considered to be present in the oxide film in the form of Cu+ and Cu ions. (the proportions of Cu+ and Cu is not known).

Meanwhile, Sb takes the form of Sb and Sb (mainly Sb in the oxide film, but the effect of enhancing the resistance against the initial rust formation is attributed to Sb ion, as mentioned before.

However, Sb itself is reduced to Sb through its oxidation of Fe ion into Fe ion, and is oxidized by C11 ion also present in the oxide film according to the reaction:

By the above reaction the resistance against the initial rust formation is enhanced.

Considering also from the ion radius, ions of higher atomic valence like Sb or Cu are easier to exist in the iron oxide, and Sb is more 'stable than Cu in the oxide, and thus the presence of Cu ion gives a large effect on the resistance against the initial rust formation.

When copper is present in an amount more than intermetallic compounds or copper phase is caused to precipitate, which causes the fonmation of local cells which in turn cause corrosion, thus lowering the resistance against the initial rust formation.

It is already known that antimony content or antimonycopper content in steels is effective for acid resistace, particularly resi'stace against sulfuric acid. However an oxide film on the steel surface is easily dissolved and removed off in an acidic solution, and thus the corrosion reaction in such a medium proceeds in an electro-chemical reaction in which iron dissolves (Fe=Fe +-|-2e) in the anodic reaction and hydrogen generates (2H++2e=H in the cathodic reaction. In this case, therefore, it is enough to suppress either one or both of the iron dissolution and the hydrogen generation in order to inhibit the corrosion. The eifect of Sb-Cu on the acid resistance derives from its suppressing effects on the both reactions, which are considered to be due to the presence of the SbCu intermetallic compounds.

The rust prevention in the present invention that the rust formation is prevented by stabilizing the oxide film itself through the above mentioned mechanism in corrosive media where corrosion proceeds under the presence of an oxide film is completely different from that of acid resistant steels in its object and mechanism.

Further, in the present invention the remarkable resistance against the initial rust formation is assured by addition of molybdenum nickel and zirconium, and if the steel sheet is used for production of cans for carbonated beverages the relation of S/P 1 is retained so that the sulphur content in the steel sheet is effective for suppressing corrosion by the carbonated substances and at the same time the initial rust formation and the surface rust of the steel sheet are prevented by the action of S bCu content. Therefore, the technical thought of the present invention is clearly diiferent from that of conventional acid resistant steels. Meanwhile the addition of copper in single exhibits no substantial efiect as clearly shown in FIG. 1 (see 3).

As above described, the steel sheet according to the present invention has a very stable and dense oxide film formed thereon, and the oxide film is stable and no Fe ion dissolves into a paint film even when lacquering and an anodic treatment such as an electrodeposition of paint, for example, are given to the steel surface, and thus a 7 very excellent corrosion resistance even after lacquering and painting is obtained.

The reasons for limitations of elements other than antimony (bismuth) and copper in the present invention will be set forth hereinunder.

Carbon is useful only for obtaining the required mechanical strength, but tends to deteriorate the resistance against the initial rust formation. Namely, as clearly shown in FIG. 5, carbon shortens the autoreduction time and damages the stability of oxide film, and thus carbon should be not more than 0.12%, preferably not more than 0.10%. Lowering of the carbon content may be done by a vacuum degassing treatment during the steel making process or by a decarburization annealing during hot and cold rolling processes.

Manganese is added chiefly for preventing hot embrittlement due to sulphur, and is controlled between 0.l1.00% depending on the sulphur content.

For the resistance against the initial rust formation, a lower manganese content is desirable (see FIG.

Silicon should be as low as possible because it gives adverse effects on both the mechanical properties and the resistance against initial rust formation, and the silicon content is limited to not more than 0.15% in the present invention.

Phosphorus and sulphur is limited so as to meet the condition of S/P 1 in which S is 0.0150.l00% in case a special control is required by applications, particularly in case the steel contacts with substances which contain or generate carbonic acid gas and corrosion is caused by phosphoric acid, namely in case the steel is used as material for production of cans for carbonated beverages, such as Coca-Cola.

Sulphur which is present in the steel in the form of MnS corrodes into corrosive media and acts as inhibitor for the steel sheet. Although control on the contents of sulphur and phosphorus does not exert substantial influence on the resistance against the initial rust formation, it is desirable to maintain the sulphur content between 0.0l5-0.03%.

As described above, when considering the present inventive steel sheet as material for can production, resistance against corrosion by can contents is assured by the sulphur content, and the reistance against rust formation at the outer side of the can is assured mainly by antimony and copper, and thus an excellent corrosion resistance as can material is assured by the combined effects.

Zirconium, nickel and molybdenum produce only a little effect if they are added in single, but their effects are remarkably enhanced if contained under the presence of antimony. Their contents less than 0.01% are not effective while their contents more than 0.3% cause material em'brittlement and their effects tend to saturate, thus causing a considerable economical waste, as seen in FIG. 6. Therefore, their contents are limited to 0.01- 0.30% for each element in the present invention, and their preferable ranges are 0.060.10% for zirconium, ODS-0.15% for nickel and 0.030.08% for molybdenum. Combined addition of zirconium nickel and molybdenum also exerts similar effects and the total amount of zirconium nickel and molybdenum less than 0.6% is enough.

The factthat when the present inventive steel sheet is used as substate for metal plating or conversion treatments such as a phosphate treatment, remarkably improved corrosion resistance at the plated surface in the atmospheric air is obtained is well understood from the fact that the resistance against rust formation on the steel surface at pinholes of the plating layer is high.

The present invention will be well understood from the following embodiments.

Example 1 tained by reducing the carbon content of the steel of 8 basic composition prepared in a converter to less than 0.01% with a vacuum degassing and adding required alloying elements. Their corrosion resistance is shown by way of their rust resistance and their corrosion resistance after lacquering.

The relation between the corrosion resistance and elements other than carbon is explained under.

Specimen 1 is an ordinary steel, and Specimen 2 is a weather resistant steel containing increased amounts of copper and phosphorous. Their resistance against the initial rust formation is poor and their corrosion resistance after lacquering is bad. Specimens 3, 4 and 5, in which rust resistance and corrosion resistance after lacquering are improved to some extent by the addition of antimony or antimony and molybdenum, exhibit only unsatisfactory corrosion resistance due to the excessive content of copper.

Specimens 6 and 7 which are the steels according to the present invention exhibit very excellent rust resistance and corrosion resistance after lacquering due to the copper content which is limited to 0.08-0.10% and the addition of antimony, molybdenum nickel and zirconium.

Example 2 Table 3 shows corrosion resistance of the present inventive steels (Specimens Nos. 3, 4, 5, 7, 8, 9 and 10). Specimens Nos. 1 to 5 are prepared by adding alloying elements such as antimony, molybdenum, nickel, and zirconium to steel melt in a converter, with a carbon content level as seen in soft steel. Specimens Nos. 6-10 are prepared by lowering carbon content with a vacuum degassing treatment and adding alloying elements such as antimony, molybdenum, nickel and zirconium, and all of the specimens are Alskilled steel. Specimen No. 1 is a comparative steel in which the alloying element is not added. By Specimens Nos. 2 and 6 the effect by the addition of antimony alone is shown, and by Specimens Nos. 3, 4, 5, 7, 8, 9 and 10, the corrosion resistance obtained by the combined addition of antimony, molybdenum, nickel and zirconium is shown.

From Table 3 it is clear that steels containing a lower carbon content show better corrosion resistance, and steels containing copper and antimony and steels containing one or more of molybdenum, nickel, zirconium in addition to copper and antimony show excellent corrosion resistance.

Example 3 Table 4 shows steel compositions and their corrosion resistance when used as steel sheet for carbonated beverage cans.

Evaluation of the corrosion resistance is made as under.

(1) Corrosion resistance of can inside.Specimens were immersed in a commercially available phosphate carbonated beverage at 27 C. for 4 days and corrosion rate was determined by measurement of weight loss.

(2) Corrosion resistance of can inside.Specimens were stacked in a humidity cabinet (30 C., relative humidity) for one month and red rust formation (percent) on the specimen surfaces were observed.

(3) General evaluation-Corrosion resistance on can inside and outside of specimens was classified into several ranks and general evaluation was made on the base of the can inside corrosion and the can outside corrosion.

Smaller values indicate better corrosion resistance as material for can production.

In Table 4, Specimens No. 1 and Nos. 11-15 are the present inventive steel, which were produced according to conventional production processes for cold rolled steel sheet including steel making in a converter, cogging, rolling and so on.

Of the specimens set forth in Table 4, Specimen No. 2 contain no antimony and shows poor corrosion resistance on can outside, and Specimen No. 4 shows still poor corrosion resistance on can outside due to the increased content of copper. Although Specimen No. 3 shows slightly Remarks: improved corrosion resistance on can outside by the addition of antimony as compared with Specimen No. 4, Ranking its general evaluation is still unsatisfactory due to the mgh of copper- Can inside Can outside In Spec1mens Nos. 5-8, the ratio of 8/1 1s less than 1 and the corrosion resistance on can outside is a medium Mom; Ranking Percent Ranking grade, but the corros1on res1stance on can 1ns1de is poor, thus these specimens are not satisfactory as material for Less than 1 Less than L 1 can production. 10 Less than 20. 2 Less than 2. 2 In Specimens Nos. 9 and 10 the ratio of 8/1 is more Less than 30 3 13:3 2:: 2 than 1, but no antimony is added and the corrosion 5- g resistance on can outside is poor. Thus these specimens 7 are not satisfactory. 3 Specimens No. 1 and Nos. 11-15 are prepared from 10 the present inventive steel, which contain antimony and maintain the copper content in a lower side, with the ratio of S/P being more than 1, exhibit excellent corrosion resistance both on can inside and can outside, thus very What is claimed is: excellent material for can production. 1. A cold rolled steel sheet for the manufacture of car- The present invention should not be limited to the bonated beverage cans, having a stable oxide film formed above examples and various modifications and alterations thereon and having excellent resistance against initial can be made without departing from the scope of the rust formation as well as against corrosion after lacquerpresent invention. ing, consisting essentially of CO.12%, 0.1-1.00% Mn,

TABLE 2.STEEL COMPOSITIONS, RUST RESISTANCE AND CORROSION RESISTANCE AFTER LACQUERING Corrosion resistance 01181111001 compositions, percent by weight Rust after .esistance lacquering Specimen number C S1 Mn P S Cu Sb Mo Ni Zr (month) (mm.)

Comparative steel:

1 Evaluation of the rust resistance was made by stacking specimens in a humidity box at 30 0., 85% humidity, and the period until red brownish rust is formed over the whole of a clean steel surface Without rust was measured.

2 The corrosion resistance after lacquerin'g was determined by applying a phosphate treatment to a steel sheet, coating an amino-alkyd paint thereon, iscratching the paint coating, subjecting the sheet to a salt spray test (30 days) and measuring the width of blistered coating layer at the scratched por- TABLE 3.STEEL COMPOSITIONS, RUST RESISTANCE AND CORROSION RESISTANCE AFTER LACQUERING Corrosion resistance Rust after resistance lacquering Specimen number 0 S1 Mn P S Cu Sb M0 N1 Zr (month) (mm.)

Comparative steel 1 0.06 0.01 0. 36 0.017 0 011 0. 04 1.0 30 Inventive steel:

2 0. 05 0. 01 0. 29 0 012 0.018 0.06 0.110 9. 0 15 O. 05 0. 01 0. 27 0 014 0. 011 0. 08 0.072 10. 0 18 0.07 0.01 0.31 0 015 0.012 0.09 0.065 11.0 15 0.06 0. 01 0.25 0 013 0. 015 0.08 0.069 11.0 12 0. 006 0. 01 0. 28 0 008 0.010 0. l0 0. 132 10. 0 13 0. 005 0. 01 0.26 0 011 0. 013 0.09 0.081 10. 0 15 0.006 0. 01 0. 25 0 013 O. 011 0. 09 0.059 11. 0 12 0.008 0. 01 0. 27 0 011 0.014 0.10 0.076 11. 5 12 0.007 0.01 0.26 0 008 0.009 0.09 0.071 12.5 10

TABLE 4.-STEEL COMPOSITIONS AND CORROSION RESISTANCE Corrosion resistance Evalua- Chemical compositions, percent by weight Can inside Can outside tion of total Specimen number 0 Si Mn P S Cu Sb Mo A./crn. Ranking Percent Ranking ranking Inventive steel 1 0. 11 0 01 0.40 0.013 0.029 0.03 0.040 16 (2) 4 (4) 6 Comparative steel:

1 1 Si0.15%, 0.015-0.10% S, 0.01-0.20% Cu, 0.01-0.20% Sb, and S and P under the condition of S/P 1, with the balance being iron and unavoidable impurities.

2. A cold rolled steel sheet for the manufacture of carbonated beverage cans, having a stable oxide film formed thereon and having excellent resistance against initial rust formation as well as against corrosion after lacquering, consisting essentially of C0.12%, 0.1-1.0% Mn, Si 0.15%, 0.0150.10% S under the condition of S/P 1, 0.01O.20% Cu, 0.01-0.20% Sb, and at least one selected from the group consisting of Zr, Mo, and Ni in an amount of 0.010.30%, with the balance being iron and unavoidable impurities.

3. A cold rolled steel sheet according to claim 1 in which the copper content is 0.08-0.15%.

References Cited UNITED STATES PATENTS 10 CHARLES N. LOVELL, Primary Examiner U.S. Cl. X.R. 

